A distribution feeder circuit branches electrical circuits from a substation such that power from the substation may be distributed over the branches created by the distribution feeder circuit. A protective device may open the distribution feeder circuit in response to an electrical fault to prevent or reduce damage to the distribution feeder circuit, electrical apparatus or systems connected to the distribution feeder circuit, real property, or personnel in the immediate vicinity of the electrical fault. Some distribution feeder circuits include multiple protective devices that sectionalize the distribution feeder circuit, and that each open the distribution feeder circuit when a fault is detected on a corresponding section of the distribution feeder circuit. The opening of the distribution feeder circuit by a protective device de-energizes a portion of the distribution feeder circuit beyond the protective device. The fault and associated arcing may be cleared by opening a protective device. The protective device tests whether the fault has been cleared by reclosing and re-energizing the sectionalized portion of the distribution feeder circuit. If the fault has been cleared, the protective device remains closed, and a downstream section of the feeder is re-energized, thereby restoring power to connected loads. If the fault has not been cleared, then the protective device may once again attempt to clear the fault by opening. If repeated attempts to clear the fault fail, the protective device goes to a “lock out” condition in which human intervention is needed to reclose the protective device.
The action of de-energizing the distribution feeder circuit or sections thereof removes the source of power to single and three phase electrical loads serviced by the de-energized distribution feeder circuit or the sections thereof. When the circuit is re-energized, the sectionalized portion of the distribution feeder circuit experiences higher than normal loads, due to a lack of load diversity and higher electrical currents caused by the re-energization of electrical motors and transformers, which is referred to as cold load inrush. Excessively high inrush currents may cause other protective devices downstream of the sectionalized portion of the distribution feeder circuit to reopen the distribution feeder circuit even though a new fault has not occurred.
In order to prevent excessively high inrush currents from causing additional unwanted service interruptions, utility personnel may be dispatched to each of the protective devices downstream of the sectionalizing protective device to manually open the protective devices prior to re-energizing the distribution feeder circuit in an operation known as manual sectionalizing. After the distribution feeder circuit is manually sectionalized, the distribution feeder circuit is progressively re-energized starting at a section protected by a protective device immediately up-stream from the fault and proceeding section by section to the protective device farthest from the source of electrical power in a process is known as picking-up load. Load pick-up is aided by a procedure known as cold load pick-up (CLPU), which requires an operator to manually re-energize the distribution feeder circuit at each protective device that was manually opened. One method requires the operator to place an operating handle on the protective device in the “Close with Cold Pick-up” position for a short period of time, usually five to 10 seconds. A second method requires the operator to manually close the circuit by depressing a “close” button. A CLPU electronic circuit then assumes control of the protective device for a period of time during which the protective characteristics of the control mirror the feeder inrush characteristics and prevent a trip due to inrush but not a trip in response to a true fault.